1. Field of the Invention
The present invention relates to a general-purpose lead working machine for performing various working processes such as lead forming in the fabrication of semiconductor devices.
2. Description of the Related Art
The fabrication of plastic-molded semiconductor devices includes the steps of placing semiconductor chips on leadframes, molding them with plastic and performing the necessary working processes such as resin removal, dam bar cutting, lead tip cutting and lead forming. The lead working machine is used at this post-molding processing stage to perform lead forming and various other working steps.
The lead working machine is usually operated with more than one die. The working operation is performed in two different ways: in one case, the leadframe is worked as it is transported in strip form and piece parts are separated from it at the final stage, and in the other case, lead cutting and dam bar cutting are first conducted and then the product portions are separated as piece parts from the leadframe and transported to the bending step. The primary reason for adopting these two different methods of transport is as follows: in the case where the leadframe is transported in a strip form, a simple transport apparatus will do since the top and bottom rails of the leadframe can be utilized as transport guides; however, with product portions that are not suspended from the top and bottom rails by means of hanger pins (i.e., pinch leads for suspending the packages) or with products that are suspended by means of hanger pins but which may drop during transport owing to the insufficient strength of the pins, transport of the leadframe for bending or otherwise working the leads is sometimes impossible unless it is separated into piece parts.
FIGS. 19, 20 and 21 are illustrations showing the layout of a prior art lead working machine. FIG. 19 shows an apparatus that performs working processes up to the bending stage as a leadframe in a strip form is fed consecutively with pins inserted into the rail holes in the leadframe. In this apparatus, the leadframe generally indicated by 5 is worked as it is supplied from the left side of the apparatus into a first die 7 and a second die 8 on a platform 6. A feed unit 10 which allows the leadframe to be fed consecutively with pins inserted into the rail holes is positioned parallel to the train of dies. In the final step following the bending process, piece parts 11 are separated, transported from the second die and placed in a receiving portion 12. The unwanted frame which remains after the separation of piece parts 11 is directly ejected from the second die to fall free. Depending on the relationship between the number of working processes and the number of chips on the leadframe, three or more dies may be arranged side by side for working the leads.
The working machine shown in FIG. 19 is useful with DIP, ZIP, SOJ, PLCC and all other products that have hanger pins. It is particularly suitable for use with TSOPs, where it is difficult to effect precise positioning with reference to the lateral sides of the thin packages into which the leadframe has been separated.
FIG. 20 shows a working machine that has a first die 7 and a second die 8 arranged in a direction normal to the supply of the leadframe 5. In the first die 7, the leadframe is transported as while working processes such as dam bar cutting and lead tip cutting are effected and, at the final stage, the leadframe piece parts are separated from the leadframe; the piece parts then leave the first die 7 in an orthogonal direction and enter the second die 8, through which the piece parts are fed consecutively for further working. In the second die 8, the piece parts are fed consecutively by sliding them over the die by means of a feed bar 14 so that the leads are bent successively and thereafter placed in the receiving portion 12. The unwanted frame 15 is directly ejected from the first die 7. A feed bar transport unit 16 is located parallel to the second die 8.
The working machine shown in FIG. 20 is useful with DIP, ZIP, SOJ, SOP and other products that have outer leads attached in one or two directions. Because of the structural design of the bending die, this type of working machine allows for precise positioning by lateral movement and, hence, it is especially suitable for use with SOP and SOJ.
FIG. 21 shows a case in which the leadframe is transported through a first die while working processes such as dam bar cutting and lead tip cutting are carried out and, at the final stage, piece parts 11 are separated from the leadframe; thereafter the piece parts 11 emerge from the first die 7 in a direction normal to the transport through said die and are successively transported by suction to pass through a second die 17, a third die 18 and a fourth die 19 for working the leads. For transporting the piece parts 11 between successive dies, a suction transport unit 20 is provided parallel to the second die 17, third die 18 and fourth die 19. The apparatus shown in FIG. 21 requires as many dies as the steps of the bending process.
The working machine shown in FIG. 21 is useful with QFP, PLCC and other products that have outer leads attached in four directions. It is particularly suitable for use with QFP and PLCC, which are large packages that may drop while they are transported, because they are engaged by means of hanger pins.
As is apparent from the foregoing description, the conventional lead working machines perform the intended operations with a suitable method of transport being selected in accordance with the type of product to be yielded. For example, TSOP is suitably transported on a leadframe basis; SOP and SOJ are suitably transported by means of a feed bar; and QFP and PLCC are suitably transported by suction. Therefore, different types of products have to be worked by machines that are adapted for the respective types. However, providing separate working machines for different types of products is very disadvantageous from the viewpoint of manufacturing cost and, in addition, with the recent trend in the semiconductor industry toward the fabrication of many kinds of products in small lots, there has been a growing need for general-purpose working machines that are adaptable for common use in the working of different types of products.